It is well known that concrete is strong in compression, but has relatively low tensile strength. Concrete members which are subjected to tensile stress where it must be avoided or minimized are ordinarily reinforced with steel bars and/or high-strength steel wire fabric or mesh. In this manner, the steel, which is strong in tension, makes up for the deficiency of tensile strength in concrete. Except for the addition of bars and mesh, tensile strength has frequently been ignored in concrete design calculations because its effect is small in comparison to its compressive strength. In a concrete floor, for example, design focus to improve tensile resistance has been directed solely to provision of embedding longitudinal reinforcing steel bars and/or mesh in the tensile side of the slab. The bonding strength between the typical roughened surface of the steel and the concrete compensates for the lack of other means to increase tensile strength of the slab.
In machinery-supporting floors, T-slotted anchor rails which are fabricated by longitudinal welding of separate channels, I-beams, etc. are typically embedded with their slotted anchoring surfaces generally flush with the concrete floor. Machines are then fastened to the floor with bolts which have their nuts in the cross slots of inverted T-slots and the bolt shanks extend upwardly through the vertical slot formed by the T. Because of the rails being fabricated from multiple elongated members, it is difficult to keep them straight, level and accurate over long distances, e.g., in excess of fifty feet or so. Reduced accuracy of the rail anchoring surfaces requires extra time and effort in positioning the equipment. Such rails typically are capable of compressing the concrete directly beneath them under a downwardly-directed load, but offer no resistance through the concrete if an upwardly-directed tensile load is applied to the rails, e.g., if the machine must necessarily be cantilever-mounted. Oftentimes, the potential for tensile loading is compensated for by outboard supporting of the cantilevered portion of the machine directly from the concrete so as to reduce the effects of tension on the rails and surrounding concrete.